This invention relates to electric rotating machines and more particularly to electric motors having a self-starting capability.
There has been developed a line of electric motors which are small in size and yet exhibit substantial output torque. Representative motors of this type are disclosed, for example, in A. W. Haydon U.S. Pat. Nos. 3,495,113 granted Feb. 10, 1970, 3,495,111 also granted Feb. 10, 1970, 3,564,214 granted Feb. 16, 1971, 3,909,646 granted Sept. 30, 1975, 4,004,168 granted Jan. 18, 1977 and 4,087,709 granted May 2, 1978, and in A. W. Haydon and John J. Dean U.S. Pat. No. 3,770,998 granted Nov. 6, 1973. The motors customarily are of cylindrical configuration and utilize a two pole rotor and a plurality of salient stator poles arranged around the rotor to provide a nonuniform air gap therebetween. Certain of the stator poles are shaded, and this feature, together with the nonuniform air gap, results in a motor which begins rotating substantially instantaneously in response to the energization of the surrounding field coil.
Heretofore, attempts to operate such electric motors from a two-phase current supply commonly involved the arrangement of a pair of the motors side-by-side in a single housing. The rotors of the motors were mounted on the same shaft with one set of rotor poles displaced ninety degrees from the other set. With the stator poles of the respective motors in line with each other, the application of the two-phase current to the two field coils of the assembly caused the rotors to begin rotating to drive the shaft.
Such prior attempts have not been entirely successful, however, among other reasons because of the difficulty in aligning the nonsalient poles of the two rotors in fairly precise angular relationship with each other. Additional problems encountered with two-phase motors of the type previously employed resulted from the need for providing a relatively complex stator pole structure, and the motors included an unnecessarily large number of component parts which were difficult and expensive to manufacture and assemble. A further problem that has been of particular moment with respect to both the two-phase as well as single phase fractional horsepower motors was the difficulty of providing high output torque while at the same time maintaining the overall size of the motor at a minimum.